1. Field of the Invention
An embodiment of the present invention relates to a spatial light modulation unit, an illumination optical apparatus, an exposure apparatus, and a device manufacturing method. More particularly, the present invention relates to an illumination optical apparatus suitably applicable to an exposure apparatus for manufacturing such devices as semiconductor devices, imaging devices, liquid-crystal display devices, and thin-film magnetic heads by lithography.
2. Related Background Art
In a typical exposure apparatus of this type, a light beam emitted from a light source travels through a fly's eye lens as an optical integrator to form a secondary light source (a predetermined light intensity distribution on an illumination pupil in general) as a substantial surface illuminant consisting of a large number of light sources. In this specification the light intensity distribution on the illumination pupil will be referred to hereinafter as a “pupil intensity distribution.” The illumination pupil is defined as a position such that an illumination target surface becomes a Fourier transform surface of the illumination pupil by action of an optical system between the illumination pupil and the illumination target surface (a mask or a wafer in the case of the exposure apparatus).
Beams from the secondary light source are condensed by a condenser lens to superposedly illuminate the mask on which a predetermined pattern is formed. Light passing through the mask travels through a projection optical system to be focused on the wafer, whereby the mask pattern is projected (or transferred) onto the wafer to effect exposure thereof. Since the pattern formed on the mask is a highly integrated one, an even illuminance distribution must be obtained on the wafer in order to accurately transfer this fine pattern onto the wafer.
There is a hitherto proposed illumination optical apparatus capable of continuously changing the pupil intensity distribution (and, in turn, an illumination condition) without use of a zoom optical system (see Japanese Patent Application Laid-open No. 2002-353105 (Document 1)). The illumination optical apparatus disclosed in Document 1 is configured using a movable multi-mirror composed of a large number of micro mirror elements which are arranged in an array form and an inclination angle and inclination direction of each of which are individually driven and controlled. An incident beam is deflected in a state in which the beam is divided in micro units by respective reflecting surfaces in the movable multi-mirror. The movable multi-mirror converts a cross section of the incident beam into a desired shape and size and, in turn, realizes a desired pupil intensity distribution.